This invention relates to high reliability electrical attachments between coiled leads and flat electrodes, such as strip electrodes found in implantable neurostimulator systems. The requirements for the attachment are biocompatibility, isolation from body fluids, and long-term mechanical/electrical continuity under cyclic stress.
A typical strip electrode consists of a thin, flat electrical contact of biocompatible, conductive material. A typical lead consists of a tightly wound coil of one or more helical strands of fine, fatigue resistant wire or filar elements. After attachment of the helical strand to the electrical contact, the entire assembly is potted or embedded in a flat sheet of elastomer so that only the face of the contact is exposed to body fluids.
Implantable leads are made of wires typically about 0.002 to 0.004 inches in diameter. These wires are formed into coils or helical strands about 0.015-inches in diameter. Leads are coiled so they can withstand constant flexing and bending forces as a result of body movement. Because of the very fine wire diameters, however, the resulting helical strands are difficult to attach to electrical contacts by laser welding. Crimping is the preferred attachment method. In that respect, the present invention is directed to ensuring that the crimped connection between a helical strand and an electrical contact maintains the same degree of reliability as is built into the coiled lead itself.